1. Field of the Invention
The present invention relates to a lens assembly for accommodating a plurality of lenses and an imaging device having the lens assembly.
2. Description of Related Art
There is known a lens assembly in which an imaging lens for imaging subject light to a sensor of an imaging element or the like is internally incorporated. Among such a lens assembly, there is a lens assembly in which the miniaturization is promoted by simplifying a structure of an engaging portion of a lens holder and a lens frame by providing a male screw and a female screw to be precisely screwed together in the lens holder and the lens frame, and both optical axis alignment and focus adjustment is simply performed by threading the lens frame into the lens holder. Since this structure is highly miniaturized, the lens assembly is suitable to be mounted in a portable device, a vehicle, or the like.
When a mechanism for fixing the lens frame is additionally provided in a microminiature lens assembly, a size of the lens holder increases. Accordingly, the lens frame is mostly fixed to the lens holder by an adhesive. For this reason, a small adhesive reservoir is usually provided to receive an extra adhesive.
However, in the present situation, the small adhesive reservoir may not be provided in the lens holder in keeping with the further miniaturization of a portable device in the above-described microminiature lens assembly. If the adhesive reservoir may not provided in the lens holder, the adhesive is attached to a lens surface when the extra adhesive flows into a lens portion as long as a worker does not exceptionally carefully perform an operation.
On the other hand, since the use of plastic for a case of a portable device or the like is recently increasing, it is considered to promote the simplification of assembly by caulking a part of the case through thermal caulking after members are loaded within the plastic case, so as to hold the members inside the case.
When a thermal caulking technique like a technique of JP-A-8-136783 can be applied to the above-described lens assembly, the work is further comfortable and the work efficiency is improved. However, there is an issue that a plastic lens, which becomes mainstream as a lens material, inside the lens holder may be deformed when thermal caulking is performed.
When the plastic lens is manufactured by injection molding, a finished shape of the lens becomes a D-cut shape as shown in FIG. 1 since an arrangement portion of a gate for injecting resin into a molding tool is necessarily placed within an outer shape of the lens.
FIG. 1 is views showing a plastic lens 21 of a D-cut shape and an outer appearance when the plastic lens 21 is placed in a rear end face side of a tons holder 20 provided in a lens assembly 2.
When the plastic lens 21 of the D-cut shape shown in FIG. 1 is accommodated in the rear end face side of the lens holder 20, a space is generated between the lens holder 20 and a D-cut portion of the plastic lens 21 as shown in FIG. 1. For this reason, there is an issue that the lens holder 20 is bumpy and the lens holder itself is deformed when a leading end of a tool is put around the space so as to perform thermal caulking from the rear end face side of the lens holder 20 using a caulking tool.